Preheat the oven to 150°C / 300°F (130°C fan) and line two large baking sheets with baking parchment or greaseproof paper. I like to draw three rectangle shapes onto the baking parchments using a pen, and then flip the parchment over so that the pen is on the underneath and doesn't touch the meringue. This helps to make sure all the layers of the meringue are a similar size.
Grab a large bowl, or the bowl of your stand mixer, and make sure it is free from any grease. I like to rub the bowl with white wine vinegar or lemon juice to make sure it is completely grease-free, as this will help to ensure that your egg whites whisk up well.
Place the egg whites into the bowl, along with the cream of tartar. Whisk on medium until the mixture has turned frothy, and then turn up the speed to maximum and whisk until the egg whites are white and fairly stiff.
In a separate bowl, mix the caster sugar and cornflour together. Add the sugar mix to the egg whites, one tablespoon at a time, whisking as you go. Continue to whisk the egg whites for about 5 minutes, until there are no sugar grains remaining. You can test this by rubbing a little bit of the mixture between your fingers.
When the meringue is done, pipe (or spoon) the meringue onto the baking parchment, making three similarly sized rectangles. You want them to be of a similar height, and have a very slight dip in the middle.
Bake the meringues in the preheated oven for 1 hour and 30 minutes. Do not open the oven door to check on the meringues whilst baking. Once the 1 hour and 30 minutes is up, turn off the oven and leave the meringues in the oven with the door closed for at least an additional 1 hour. You can then remove the meringues from the oven and leave to finish cooling on the tray (if necessary).
When the meringue rectangles are completely cool, it is time to make the elderflower cream filling. Pour the cream and elderflower cordial into a large bowl, and whisk on high until stiff peaks have formed.
Place one of the meringue rectangles onto a serving plate or board. It will be difficult to move the assembled pavlova onto a new serving plate. Spoon a third of the cream mixture onto the meringue rectangle, and spread out to cover the whole surface. Go right up to the edges. Place a third of the berries on top of the cream, distributing them evenly across the whole surface. Place another meringue rectangle on top of the cream and berries, and press down very gently.
Repeat the above process twice more, until you have a completed three-tier pavlova. Add a couple of sprigs of fresh mint to the top of the pavlova if wanted, and then serve.
The pavlova is best served on the day or the day after it is made. Keep the pavlova in the fridge before serving. The baked and unfilled meringue rectangles should stay fresh for up to 2 weeks if kept in an airtight tin (not in the fridge). You can then make the cream and fill on the day of serving.
Summer Berries Pavlova with Elderflower Cream https://whatcharlottebaked.com/2018/08/21/summer-berries-pavlova-with-elderflower-cream/